Angular acceleration and rolling resistance

On Jan 18, 7:45*am, "Ed Medlin" > wrote:
> "Zach" > wrote in message
>
> ...
>
>
>
> > I'm trying to understand the resulting torques that act back on the
> > axle. For a free rolling wheel travelling purely in the longitudinal
> > direction and with a slip ratio > 0, it will output a force of say
> > 100N. As well as pushing the vehicle forward it also creates a torque
> > on the axle which is then used to calculate the angular acceleration.
> > The forward velocity also creates a rolling resistance moment as a
> > function of vertical load and forward rolling speed. There is also a
> > moment produced by the internal bearing friction trying to slow it
> > down.
>
> > I understand this, however if the vehicle were to rotate
> > instantaneously such that the the longitudinal velocity = 0, the
> > longitudinal slip ratio = 0, the angular velocity > 0, and the lateral
> > velocity was 10mts/s and hence the lateral slip ratio > 0, the tyre is
> > not outputting any force in the longitudinal direction thus meaning
> > the only forces acting against the angular velocity of the wheel are
> > the internal bearing friction and rolling resistance moment. However
> > the rolling resistance moment is a function of forward rolling speed
> > which if equal to 0 there is no moment produced. Thus in the
> > simulation if travelling purely in a lateral direction in the tyre's
> > frame of reference, the only force acting against the angular velocity
> > of the wheel is internal bearing friction, however this is wrong as it
> > is not the only force acting on it. The wheel would only slow down as
> > a result of the bearing friction which is not correct There must be
> > another additional force derived from lateral slip that adds to the
> > rolling resistance moment.
>
> > In real life if a vehicle were to instantaneously rotate and travel in
> > a purely lateral direction, the wheels would stop rolling from the
> > lateral slip. I'm trying to work out what that force is. I hope this
> > post is clear. Any help is much appreciated!
>

Hi Zach :-) Guess you guys won't be using my tire model after all
then, eh? ;-)

Just to make sure I understand: You're talking about simply moving
the tire sideways (90 degree slip angle)? The tire should not spin
indeed of course. The force that will cause this is just the
longitudinal force from slip ratio. Tire rotates forward, it gets a
backwards torque. Tire rotates backward, it gets a forwards torque.
That should keep the angular velocity at or near enough to zero in
most tire models, although without a relaxation approach of some kind
it may still jitter a little bit. There isn't any "missing force"
here. What's happening wrong in the simulation? Do the wheels
continue to spin even at 90 degrees slip angle?

Concerning the other posts: There is indeed a change in rolling
resistance with slip angle. Also with slip ratio. The example of an
IndyCar losing speed doesn't have much to do with that, though.
That's induced drag caused by the component of the lateral force
pointing rearwards because there's a slip angle, which slows the car
down. Two different things, and I suspect that's not really what Zach
was asking about. Correct me if I'm mistaken..